1. Field of the Invention
The invention relates to an electroluminescent display, and more particularly, to an electroluminescent display having a brightness enhanced film that can increase brightness gain and reduce image blur.
2. Description of the Prior Art
Flat displays have advantages, such as saving electricity, low radiation, small size, etc., over the traditional cathode ray tube (CRT) displays. For these reasons, flat displays are replacing CRT displays gradually. With the improvements of flat display techniques, the prices of flat displays are getting lower. Therefore, flat displays are more popular and undergoing developments for larger sizes. The electroluminescent display is a most remarkable product among the flat displays at present because of having an advantage of high contrast.
Please refer to FIG. 1. FIG. 1 is a schematic diagram of a conventional electroluminescent display. As shown in FIG. 1 the conventional electroluminescent display 10 includes a lower substrate 12, an upper substrate 14, a plurality of illumination components 16 disposed between the lower substrate 12 and the upper substrate 14, and an encapsulation layer 18 disposed between the lower substrate 12 and the upper substrate 14 so as to encapsulate the illumination components 16 between the lower substrate 12 and the upper substrate 14.
Each illumination component 16 includes an anode 20, a cathode 22 and an organic luminescence layer 24 disposed between the anode 20 and the cathode 22. While displaying images, a voltage difference exists between the anode 20 and the cathode 22 of the illumination component 16. Holes will enter the organic luminescence layer 24 having a characteristic of illumination via the anode 20, and electrons also will enter the organic luminescence layer 24 via the cathode 22. When holes and electrons recombine in the organic luminescence layer 24, excitons will be formed. At the same time, the excitons are in a high energy and unstable state. When the excitons return to the stable ground state, the energy of the excitons will be released. Depending on different illumination materials of the organic luminescence layer 24, the energy will be released in the types of the light of different colors so as to produce radiation of the illumination component 16.
While displaying images, the light produced by the illumination component 16 will be emitted to the lower substrate 12. Because the refractive index of the lower substrate 12 (usually being a material of glass) is different from the refractive index of the external environment, the light L will have phenomenon of refraction and reflection when passing through the downward surface of the lower substrate 12, that is, the interface of the lower substrate 12 and air. As shown in FIG. 1, when the light is emitted to the downward surface of the lower substrate 12, the light L having the incident angle smaller than the critical angle c will be refracted and be emitted out to be effective light Le. When the incident angle is larger than the critical angle c, the total reflection effect will happen. The light will be totally reflected by the downward surface of the lower substrate 12 to be ineffective light Li. In the light L emitted by the illumination component 16, the ineffective light Li cannot pass the lower substrate 12 so that the illumination efficiency of the conventional electroluminescent display 10 is lower. Therefore, it is necessary to increase the illumination efficiency further.